I've never seen spa prices posted on cruiseline websites, but my general experience is that prices are almost double on board ship. For example, I routinely pay $60-70 for a one-hour massage in San Francisco, whereas that would be $110-120 on a ship. Plus Steiner adds an automatic 10% gratuity - don't know whether other spa companies add a tip.

In fairness, the spa staff who work on ships are highly trained and professional.

Average prices on the Voyager class ships run $90 for a full body massage or facial. Actual price can vary and you will need to wait until you get onboard and check with the spa - watch for the specials that they promote throughout the week on various services.
Nancy